Phosphino-phenolate neutral nickel catalysts 1–3/B(C6F5)3, without the help of any organoaluminum compound, were found to be efficient catalytic systems for norbornene polymerization and its copolymerization with norbornene derivatives. The amount of B(C6F5)3 required for achieving a high efficiency (3 equiv.) was markedly lower compared to previous reports, and high molecular weight polymers were obtained (>106 g mol−1). Efficient incorporation of polar monomers NBC, NBA, and NBM was also achieved in a controllable fashion, yielding high molecular weight copolymers. Catalysts 1–3 were highly active for ethylene polymerization as single component catalysts, with an activity of up to 107 g molNi−1 h−1, and catalyst 3 was more readily initiated at lower temperature. Catalysts 1–3 were also efficient in incorporating norbornene (up to 30%) into the polyethylene backbone. Bisligated phosphino-phenolate nickel complex 4 and salicylaldimine complex 5 were also studied for comparison, which further verified the unique performance of catalysts 1–3. Preliminary NMR analyses were conducted to explore the norbornene polymerization mechanism.

•A series of novel [ONNO]-type oxovanadium(V) complexes were synthesized and characterized.•These complexes contain two isomers, and trans configuration proved to be the main isomer.•These catalysts displayed efficient catalytic behavior toward ethylene (co)polymerization.•Catalytic property was significantly influenced by catalyst structure and reaction conditions.A series of oxovanadium(V) complexes bearing dianionic [ONNO] chelate ligands 2-[bis(3-R1-5-R2-2 -hydroxybenzyl) aminomethyl]pyridine (2a: R1 = tBu, R2 = H; 2b: R1 = CF3, R2 = H; 2c: R1 = OCH3, R2 = H; 2d: R1 = R2 = tBu) and 2-[bis(3-R1-5-R2-2 -hydroxybenzyl) aminoethyl]pyridine (2e: R1 = R2 = tBu) have been synthesized by reacting VO(OnPr)3 with 1.0 equiv. of the ligands in CH2Cl2. All these complexes were characterized by 1H, 13C, 51V NMR spectra and elemental analysis. X-ray structural analysis for 2d revealed a six-coordinate distorted octahedral geometry around the vanadium center in the solid state. It was observed that these complexes existed as a mixture of two isomers, and the main isomer had the oxo moiety in trans configuration to the tripodal nitrogen atom. In the presence of Et2AlCl and CCl3COOEt, these complexes displayed high catalytic activities for ethylene polymerization even at elevated reaction temperature, depending on ligand structures. The resultant polymers possessed high molecular weights and unimodal molecular weight distributions, indicative of a single active site nature. In addition, copolymerizations of ethylene and norbornene using precatalysts 2a–e were also investigated, and the observed catalytic activity was nearly comparable with that for ethylene homopolymerization. When the concentration of comonomer in the feed amounted to 3.0 mol/L, a NBE incorporation up to 41.5% could be achieved. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature and Al/V (molar ratio), are also examined in detail.

•Neutral nickel catalysts based on dimethylxanthene frameworks were synthesized.•The binuclear catalyst is more thermally robust than mononuclear analogue.•The binuclear catalyst showed improved catalytic activity for ethylene polymerization.•The binuclear catalyst displayed enhanced efficiency in the copolymerization.Mononuclear neutral nickel catalyst Ni1 and binuclear complexes Ni2 and Ni3 based on rigid 9,9-dimethylxanthene frameworks featuring short Ni−Ni distances were synthesized, characterized and applied in ethylene (co)polymerization. Binuclear catalyst Ni2 exhibited higher activity in ethylene polymerization than corresponding mononuclear Ni1, and produce higher molecular weight polymer with a bimodal molecular weight distribution. Catalyst Ni2 is remarkably thermally robust, and still displaying promising activity at 93 °C. The polymer microstructure produced by Ni1 reveals a hyperbranched structure with a variety of branch types, while Ni2 product features methyl branches primarily. In the presence of comonomer 1,5-hexadiene, 1,7-octadiene, and methyl 10-undecenoate, mononuclear Ni1 suffers from either low catalytic activity or poor incorporation efficiency, while binuclear catalyst Ni2 effectively enchained these comonomers into the polymer chain, giving copolymer with unique microstructures.

Phosphino-phenolate neutral nickel catalysts 1–3/B(C6F5)3, without the help of any organoaluminum compound, were found to be efficient catalytic systems for norbornene polymerization and its copolymerization with norbornene derivatives. The amount of B(C6F5)3 required for achieving a high efficiency (3 equiv.) was markedly lower compared to previous reports, and high molecular weight polymers were obtained (>106 g mol−1). Efficient incorporation of polar monomers NBC, NBA, and NBM was also achieved in a controllable fashion, yielding high molecular weight copolymers. Catalysts 1–3 were highly active for ethylene polymerization as single component catalysts, with an activity of up to 107 g molNi−1 h−1, and catalyst 3 was more readily initiated at lower temperature. Catalysts 1–3 were also efficient in incorporating norbornene (up to 30%) into the polyethylene backbone. Bisligated phosphino-phenolate nickel complex 4 and salicylaldimine complex 5 were also studied for comparison, which further verified the unique performance of catalysts 1–3. Preliminary NMR analyses were conducted to explore the norbornene polymerization mechanism.